Let us Cover the World!

CubeSats are a 10cmx10cmx10cm satellites which orbit the Earth in a LEO (Low Earth Orbit between 200km and 2000km). They transmit data constantly from around the globe but can only have this information downloaded when passing over a ground station.

A ground station is like an antenna, picking up the Satellites signal and downloading the payload information. The payload can be anything from a camera to a specially designed experiment, as long as it fits inside the CubeSat!

Below is a block diagram of a LEO class 1 ground station, these are the ground stations that will be used.

Either by using your own knowledge of the Electromagnetic Spectrum of light, or by researching It, What Part of the EM spectrum can the antennas detect?

Answers: Microwave

We know from other Ground stations that the usual visibility time (footprint) for downlink is about 10 minutes.

The average orbital velocities of the CubeSats are 7.5km/s.

  1. What is the Diameter of the area of this footprint? (HINT: Speed = Distance/Time)

Answers: Speed = distance/time, time = 10 mins = 10min x 60 seconds = 600 seconds

Speed x time = 7.5x600 = 4500km/s

  1. What is the Area in km2 of this footprint? (HINT: Area of a Circle = πr2 where r is the RADIUS)

Answers: Area = π x (4500/2)2 = 15.9x106km2 (saying 16 million km2 is accurate enough)

The idea here is to notice you are using RADIUS and not the DIAMETER as above

  1. What is the Surface area of the Earth in km2? (HINT: Surface Area of a SPHERE = 4πr2)

Answers: Radius of the Earth between 6000km and 7000km,

Area = 4 x π x 65002 = 5.3x108km2 (4.5x108< Area <6.2x108)km2

  1. What is the percentage of the Earth covered by 1 ground station?

Answers: (Area of footprint / Surface area of Earth) x 100 = (2.4%<Percentage<3.5%)

  1. Assuming none of the ground stations overlap, how many would you need to cover the satellites detection around the entire Earth?

Answers: 100/Percentage covered by one ground station = (29<Number<42)

You can’t have a percentage of a ground station so deduct points if they have put a decimal!

  1. What percentage have we covered with 8 ground stations, assuming they don’t overlap?

Answers: Percentage x 8 = (19.2%<Percentage<28%)

  1. On the map overleaf, come up with a suitable scale and draw on (using a compass) the locations for the Cardiff, Hawaii, South Africa, Australia, and Chile ground stations. Where could you place more to get a full Earth Coverage? (HINT: for the scale you could measure the distance between 2 Cities, or the length of Madagascar. You would have to mark them on first.)